A water softening apparatus removes hardness components in raw water such as tap water using an ion exchange resin bed (water softening treatment) to obtain soft water. Hardness component removing ability of the ion exchange resin bed is gradually decreased by continuous water softening treatment. Regenerating treatment of recovering the hardness component removing ability thus needs to be executed before the hardness component removing ability is lost, by causing the ion exchange resin bed to react with salt water (e.g. sodium chloride aqueous solution).
Recently provided is a water softening apparatus that automatically switches passages between raw water softening treatment and ion exchange resin bed regenerating treatment. This water softening apparatus includes a pressure tank (resin cylinder) accommodating an ion exchange resin bed configured to soften raw water, a control valve configured to automatically switch fluid passages upon switching between water softening treatment and regenerating treatment, and a salt water supply unit (salt water supply device) configured to supply the pressure tank with salt water used for regeneration of the ion exchange resin bed (see Patent Document 1).
The salt water supply unit includes, as main elements, a salt water tank, a salt water plate, a water level detecting float, a salt water well, and a salt water valve. The salt water tank accommodates a salt container configured to contain salt serving as a regenerant, and a salt water reservoir configured to reserve salt water that is generated from salt and makeup water (e.g. raw water) supplied from outside. The salt water plate is a water permeable member that partitions the interior of the salt water tank into the salt container and the salt water reservoir and allows salt to be placed on its upper surface. The water level detecting float is a member that is located inside the salt water well and is floatable on a water surface.
The salt water well is a cylindrical member that stands in the salt water tank so as to be divided from the salt container and to surround the water level detecting float. The salt water well has a communication hole (flow hole) allowing fluid to flow between the interior of the salt water well and the salt water reservoir. The communication hole of the salt water well prescribes, by its height, the maximum amount of salt water fed from the salt water reservoir into the salt water well, in other words, the maximum amount of salt water consumed by regenerating treatment.
The salt water valve is located in the salt water well and has a communication passage connecting the communication hole of the salt water well and the exterior of the salt water tank, a valve element configured to open or close the communication passage in accordance with the position of the water level detecting float, and the like. The salt water well vertically penetrates the salt water plate and is inserted to the bottom of the salt water tank (see Patent Documents 2 and 3).
The control valve switches the passages upon regenerating treatment in the water softening apparatus, so that salt water is imported from the salt water tank into the pressure tank and the ion exchange resin bed is regenerated. The salt water tank is supplied with makeup water after regenerating treatment, so as to generate salt water to be used for next regenerating treatment. Salt in the salt container dissolves in this makeup water, so that salt water of the saturated concentration is generated in the salt water tank.
Patent Document 1: Japanese Patent Laid-open Publication No. 2007-260574
Patent Document 2: Japanese Patent Laid-open Publication No. 04-108586
Patent Document 3: Japanese Patent Laid-open Publication No. 2011-31214